Treatment of thrombotic or atherosclerotic lesions in blood vessels using an endovascular approach has recently proven to be an effective and reliable alternative to surgical intervention in selected patients. For example, directional atherectomy and percutaneous translumenal coronary angioplasty (PTCA) with or without stent deployment are useful in treating patients with coronary occlusion. Atherectomy physically removes plaque by cutting, pulverizing, or shaving in atherosclerotic arteries using a catheter-deliverable endarterectomy device. Angioplasty enlarges the lumenal diameter of a stenotic vessel by exerting mechanical force on the vascular walls. In addition to using angioplasty, stenting, and/or atherectomy on the coronary vasculature, these endovascular techniques have also proven useful in treating other vascular lesions in, for example, carotid artery stenosis, peripheral arterial occlusive disease (especially the aorta, the iliac artery, and the femoral artery), renal artery stenosis caused by atherosclerosis or fibromuscular disease, superior vena cava syndrome, and occlusive iliac vein thrombosis resistant to thrombolysis.
It is well recognized that one of the complications associated with endovascular techniques is the dislodgment of embolic materials generated during manipulation of the vessel, thereby causing occlusion of the narrower vessels downstream and ischemia or infarct of the organ which the vessel supplies. In 1995, Waksman et al. disclosed that distal embolization is common after directional atherectomy in coronary arteries and saphenous vein grafts. See Waksman et al., American Heart Journal 129(3): 430-5 (1995), incorporated herein by reference. This study found that distal embolization occurs in 28% (31 out of 111) of the patients undergoing atherectomy. In January 1999, Jordan, Jr. et al. disclosed that treatment of carotid stenosis using percutaneous angioplasty with stenting is associated with more than eight times the rate of microemboli seen using carotid endarterectomy. See Jordan, Jr. et al. Cardiovascular surgery 7(1): 33-8 (1999), incorporated herein by reference. Microemboli, as detected by transcranial Doppler monitoring in this study, have been shown to be a potential cause of stroke. The embolic materials include calcium, intimal debris, atheromatous plaque, thrombi, and/or air.
There are a number of devices designed to provide blood filtering for entrapment of vascular emboli. Filters mounted to the distal end of guidewires have been proposed for intravascular blood filtration. A majority of these devices includes a filter which is attached to a guidewire and is mechanically actuated via struts or a pre-shaped basket which deploys in the vessel. These filters are typically mesh “parachutes” which are attached to the shaft of the wire at the distal end and to wire struts which extend outward in a radial direction at their proximal end. The radial struts open the proximal end of the filter to the wall of the vessel. Blood flowing through the vessel is forced through the mesh thereby capturing embolic material in the filter. These devices are self-directing and can be placed intravascularly. However, one major disadvantage associated with the current devices is that the steerability of the guidewire may be altered as compared to the conventional guidewires due to the size of the filter. The guidewire may bend, kink, and/or loop around in the vessel, making insertion of the filter through a complex vascular lesion difficult.
During endovascular procedures, it is not uncommon to exchange one endovascular device for another over the guidewire. However, the guidewire position is often lost or compromised during the exchange of devices. For example, during coronary revascularization, it is often required to exchange of one guide catheter for another guide catheter possessing different qualities, e.g., a larger diameter guide to deliver a specialized angioplasty device, a smaller diameter guide to prevent deep intubation and/or pressure damping, a different guide shape, or a guide catheter containing side holes. It is known that there are few interventional maneuvers as challenging as attempting to maintain distal guidewire access while trying to exchange one guiding catheter for another without compromising the guidewire position.
What is needed are rapid exchange sheaths which can be advanced over a guidewire and carry an endoluminal medical device to a region of interest and can thereafter be removed from a patient's vessel without requiring a large proximal guidewire segment extending out of the patient's vessel. Existing devices are inadequate for this purpose.